linux-kernel - [PATCH AUTOSEL 5.8 13/29] NFS: Zero-stateid SETATTR should first return delegation

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Message-Id: <20200914130358.1804194-13-sashal@kernel.org>
Date:   Mon, 14 Sep 2020 09:03:42 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Chuck Lever <chuck.lever@...cle.com>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Sasha Levin <sashal@...nel.org>, linux-nfs@...r.kernel.org
Subject: [PATCH AUTOSEL 5.8 13/29] NFS: Zero-stateid SETATTR should first return delegation

From: Chuck Lever <chuck.lever@...cle.com>

[ Upstream commit 644c9f40cf71969f29add32f32349e71d4995c0b ]

If a write delegation isn't available, the Linux NFS client uses
a zero-stateid when performing a SETATTR.

NFSv4.0 provides no mechanism for an NFS server to match such a
request to a particular client. It recalls all delegations for that
file, even delegations held by the client issuing the request. If
that client happens to hold a read delegation, the server will
recall it immediately, resulting in an NFS4ERR_DELAY/CB_RECALL/
DELEGRETURN sequence.

Optimize out this pipeline bubble by having the client return any
delegations it may hold on a file before it issues a
SETATTR(zero-stateid) on that file.

Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@...merspace.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/nfs/nfs4proc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 7f337188a2829..08b1fb0a9225a 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -3272,8 +3272,10 @@ static int _nfs4_do_setattr(struct inode *inode,

 	/* Servers should only apply open mode checks for file size changes */
 	truncate = (arg->iap->ia_valid & ATTR_SIZE) ? true : false;
-	if (!truncate)
+	if (!truncate) {
+		nfs4_inode_make_writeable(inode);
 		goto zero_stateid;
+	}

 	if (nfs4_copy_delegation_stateid(inode, FMODE_WRITE, &arg->stateid, &delegation_cred)) {
 		/* Use that stateid */
-- 
2.25.1